1. Field of the Invention
This invention relates generally to annealing furnaces, and more particularly to bell type annealing furnaces for annealing coils of material in a controlled atmosphere.
2. Background Information
Bell type annealing furnaces are well known in the art and have been used for many years to anneal coils to materials such as coils of steel strip or wire or rod. In essence, the annealing furnace includes a base which provides a support for the coils. A bell cover is provided which is placed over the coils and seals against the base to provide a scaled interior for circulation of inert gas or other controlled atmospheres which may be required for annealing or other metallurgical processes. A fan is mounted on the base for circulating the gas within the bell cover. An outer furnace is provided which is heated either by electricity or gas combustion and is scaled over the bell cover sometimes sealing on the bell cover and sometimes sealing on the base.
There are many considerations that go into the design and construction of these bell furnace installations. Among these considerations is included: the necessity to seal the inner bell cover against gas leakage as well as the need to seal the outer cover against air and gas, leakage and the need to accommodate thermal expansions at the elevated temperatures and especially to accommodate the thermal expansion wherein there are significant temperature gradients between different locations of the furnace structure. This must be done in a manner which is strong enough to support the coils being treated and promote maximum air flow and circulation to prevent any hot spots or heat build-ups at elevated temperatures. Moreover, the use of the same parts for different size furnaces is an important aspect of the economical construction of different size furnaces.